Either alpha-tubulin isogene product is sufficient for microtubule function during all stages of growth and differentiation in Aspergillus nidulans.

Abstract

, 1991). The tubB gene is not required for any detectable aspect of vegetative growth or asexual reproduction but is essential during sexual development prior to the first meiotic division (K. E. Kirk and N. R. Morris, Genes Dev. 5:2014-2023. In this study, we determined whether the role of each a-tubulin gene is to provide a specific isotype necessary for a particular microtubule function or whether either ct-tubulin isotype, if present in sufficient quantities, can participate effectively in all types of microtubule. Strains carrying a deletion allele of tubB (tubBA) produce no ascospores from a cross. When one copy of a plasmid containing the region upstream of the tubB gene fused to the tubA coding region was integrated into a tubBA strain, ascosporogenesis proceeded beyond the tubBA block and resulted in the formation of sexual spores. However, irregular numbers of spores formed in some asci during development, and the ascospores had greatly diminished viability and aberrant morphologies. These defects were nearly corrected when two additional copies of the tubA coding region were integrated into the tubBA strain. These results indicate that the tubA at-tubulin isotype can form functional microtubules during sexual development in the absence of tubB protein.In a reciprocal set of experiments, we examined whether upregulation of lubB can complement the tubA4 mutation, which causes supersensitivity to benomyl during vegetative growth. When tubA4 strains integrated a plasmid containing an alcohol-inducible promoter joined to the tubB coding region and subsequently overexpressed the tubB isotype, the benomyl supersensitivity normally caused by the tubA4 allele was relieved. These results indicate that when enough tubB a-tubulin is supplied, strains lacking functional tubA isotype can still form microtubules which effectively carry out mitosis and nuclear migration.

Tubulins in Aspergillus nidulans

“…Kirk and Morris (1993) performed a number of experiments changing the promoters of the two genes to answer this question. In a tubB deletion, one copy of the tubA coding sequence under the control of the tubB promoter supported ascospore formation, but ascospore number and viability were subnormal.…”

Structurally similar Drosophila alpha-tubulins are functionally distinct in vivo.

“…The answer to the question depends on the kind of organism in which one asks the question (reviewed in Raff, 1994). In fungi, even quite divergent isoforms are functionally interchangeable (at least for growth under optimal laboratory conditions), suggesting that in these organisms the first answer is primarily the correct one (Schatz et al, 1986;May, 1989;Kirk and Morris, 1993). For multicellular organisms, the situation is more complicated: patterns of tubulin gene expression coupled with functional tests reveal isoform specialization and differential gene expression as a means to control time, place, and amount of tubulin synthesis.…”

Two divergent catalase genes are differentially regulated during Aspergillus nidulans development and oxidative stress

“…A representative experiment is shown. two functionally redundant polypeptides exist to facilitate altered patterns of expression during development (22).…”